HF/UHF dual mode RFID transponder antenna and HF range extension via wireless power transmission

A novel HF/UHF compatible RFID transponder antenna is designed, simulated and measured for dual band operation and HF range increase. Dual mode compatible RFID transponder antenna enjoys the benefits of each mode and eliminates the disadvantages of single mode operation. The transponder antenna can easily be configured for either HF mode, or UHF mode only, or HF mode with UHF range extension mode.Limited range of HF RFID systems can be overcome if more power can be delivered to the transponder antenna which could not be achieved in HF band due to near-field strength regulations set by the standards. However, using UHF band, wireless power can be delivered by the reader to the HF transponder. To achieve such operation, the transponder antenna must be dual band. The rectify circuit for wireless power transmission at UHF band must also be optimized for maximum efficiency and we obtained about 63% system efficiency when measured from end-to-end. The influence of coexistence of HF and UHF antennas on the same structure are well characterized and measured to corroborate simulation results.Even though UHF RFID has benefit in having better read/write range capability, these tags can get easily affected by the surroundings or application environment such as on/near metal and plastics. When tags are placed in such environments, tag impedance can change and detune easily, and also radiation characteristics may change considerably, which, in turn, makes the UHF tag less reliable. Therefore, there is a need for an UHF RFID tag that is less sensitive to environment and is capable of preserving radiation characteristics in such environments. Although several studies which address this issue have been reported in the literature, they are all limited to dipole-like or slot dipole-like structures. We propose a microstrip antenna where its ground serves as isolation to its surroundings such that its main electrical performance metrics do not change drastically when placed on or near metallic structures. The performance of the designed antenna has been compared to that of a Texas Instruments transponder antenna, which has widespread use for many UHF applications. We prove that our transponder antenna behaves much better than TI?s antenna under a variety of typical RFID applications.